Field of the Invention
This disclosure relates to management of register storage in a processor and, more particularly, to structures and techniques for register storage management in processors that support speculative execution and register renaming.
Description of the Related Art
Register renaming is a technique commonly employed in advanced computer processor designs to avoid unnecessary serialization of program operations that might otherwise be required by resource dependencies that result from contention for, and reuse of, registers allocated to a program (e.g., by a compiler or execution environment) rather than true producer-consumer, data dependencies. By providing facilities to rename (or map) the generally smaller number of registers that are defined by an instruction set architecture (ISA) to a generally larger number of physical registers implemented in a particular realization of that ISA, it is often possible to execute some instructions of a program-order sequence of instructions in parallel and, in many cases, to complete instructions that would otherwise have to wait for their program-specified, architectural register destination target to be available. In this way, and using multiple execution units, modern computer processors can provide improved performance and throughput.
Speculative execution is another technique that is commonly employed in advanced computer processor designs to improve performance and throughput. By dispatching and executing instructions ahead of (i.e., speculatively with respect to) results or states to which a program sequence of instructions are not yet committed, a processor and computation can often make progress. If the speculative states on which speculatively executed sequence of instructions relies turn out to be correct, such as in a correctly predict branch, and if roll-back costs of being wrong are statistically tolerable, speculative execution can provide performance and throughput benefits. Checkpoint repair is one approach to managing roll-back.
Mechanisms for implementing register renaming and speculative execution in advanced computer processors can be complex and of varied design, particularly when out-of-order execution and exception handling are considered. Increased counts of architectural and physical registers, increased levels of instruction parallelism and numbers of instructions in flight at any given time, and increased register widths in modern microprocessors and processor cores all complicate the design trade-offs and challenges.
Improved designs and implementations are desired.
The use of the same reference symbols in different drawings indicates similar or identical items.